Some conventional security or surveillance cameras use varifocal lenses that allow an adjustable field-of-view. When equipped with an IR illuminator, the illumination pattern is fixed for all focal lengths and is generally optimized for a specific field of view at one focal length. For field of views that are larger than the optimized field of view, a non-optimal illumination pattern will appear as a bright spot in the centre of the image, saturating the sensor in that region and obscuring detail. Conversely, for field of views that are narrower than the optimized field of view, some of the illumination power will be projected outside of the imaging area and therefore be wasted. As a result, a less than optimal IR image is captured by surveillance cameras that use such IR illuminators.